9. Cartilage of the Joint Flashcards
what is CARTILAGE
specialized form of CONNECTIVE TISSUE that consists of CELLS and
EXTRACELLULAR MATERIAL
What do you find in CARTILAGE, EMBEDDED in ECM
CHONDROCYTES
- secrete extracellular material (mostly matrix proteins)
what gives the cartilage its unique characteristics
MATRIX
CARTILAGES are classified into: (3)
- HYALINE CARTILAGE
(mainly in Synovial Joints) - ELASTIC CARTILAGE
(outer ear, larynx, epiglottis) - FIBROCARTILAGE
weight-bearing
(pubic symphysis, intervertebral discs, meniscus, and temporomandibular joint)
what do you find in ELASTIC CARTILAGE (in matrix)
ELASTIC FIBRES in matrix
what do you find in the MATRIX of FIBROUS CARTILAGE
COLLAGEN FIBRES
COMPONENTS of CARTILAGE (3)
COLLAGEN
ELASTIN
PROTEOGLYCAN
which COLLAGEN is the main one in CARTILAGE
TYPE 2
PURPOSE of COLLAGEN in CARTILAGE
provide structural STRENGTH
- therefore type 2
PURPOSE of ELASTIN in CARTILAGE
FLEXIBILITY
PURPOSE of PROTEOGLYCAN in CARTILAGE
provides LARGE OSMOTIC EFFECT
how do PROTEOGLYCANS in CARTILAGE provide LARGE OSMOTIC EFFECT
- they carry many NEGATIVE CHARGES
- ATTRACT CATIONS (+) eg Na2+ SODIUM
- resulting in LARGE OSMOTIC EFFECT which HOLDS WATER in the MATRIX (flow of water from the weak solution to the strong solution - WATER IN, enhances ability to BEAR LOAD)
What is a PROTEOGLYCAN
- PROTEOGLYCANS consist of a core protein with at least one GLYCOSAMINOGLYCAN (GAG) COVALENTLY LINKED
Glycosaminoglycan: long
unbranched polysaccharide chains composed of repeating disaccharide units
EXAMPLE of a major PROTEOGLYCAN in CARTILAGE
AGGRECAN
what joint related substance is a NONSULFATED GLYCOSAMINOGLYCAN
HYALURONIC ACID
What is the MAIN FUNCTION of CARTILAGE
CONNECT BONES TOGETHER
(also found in the joints, the rib-cage, the ear, the nose, the throat and between the bones of the back)
another FUNCTION of CARTILAGE
create a place on which BONES CAN FORM when they are first developed
- growth plate
structure of the ECM of ELASTIC CARTILAGE
CRISS-CROSSED by numerous BRANCHED ELASTIC FIBRES - rich in ELASTIN (protein)
(see image)
ELASTIC FIBRES in ELASTIC CARTILAGE have a HIGH DEGREE OF FLEXIBILITY and RESILIENCE.
what % of their orginial length:
150% of ORIGINAL LENGTH
When bent, elastic cartilage will rapidly bounce back to its original form
what do you find on the OUTER MARGINS of ELASTIC CARTILAGE
fibrous PERICHONDRIUM
- made of dense connective tissue (collagen secreted by FIBROBLASTS)
where is ELASTIC CARTILAGE MAINLY FOUND (3)
- EXTERNAL EAR
- EUSTACHIAN TUBES (opening that connects the middle ear with the nasal-sinus cavity)
- epiglottis (flap of tissue that sits beneath the tongue at the back of the throat)
what does FIBROCARTILAGE compose of
TYPE I COLLAGEN
& FIBROUS TISSUE
viewed as a composite/mixture of HYALINE CARTILAGE
and DENSE FIBROUS CONNECTIVE TISSUE (COLLAGEN I)
what does FIBROCARTILAGE LACK
a true PERICHONDRIUM
FUNCTION of FIBROCARTILAGE
what sort of sites is it found at
WEIGHT-BEARING
at sites which are subjected to TENSILE and COMPRESSIVE FORCES
forms a structural and functional junction
where cartilage and ligament meet
where is FIBROCARTILAGE FOUND
INTERVERTEBRAL DISCS
MENISCI of KNEE (Lateral & Medial)
TEMPOROMANDIBULAR JOINT
ARTICULAR CARTILAGE is which type of cartilage
HYALINE
2 FUNCTIONS of HYALINE CARTILAGE
- DISTRIBUTE LOAD
(shock absorb) - ALLOW MOVEMENT
in HYALINE CARTILAGE, COLLAGEN TYPE II is ATTACHED to COLLAGEN TYPES..
9 IX
& 11 XI
MATURE CHONDOCYTES (in hyaline and elastic cartilage) occupy spaces in the MATRIX called
LACUNA
2 CHARACTERISTICS of ARTICULAR CARTILAGE
AVASCULAR (no blood supply)
ANEURAL (no nerves)
ARTICULAR CARTILAGE is..
SHOCK-ABSORBING
cells in the matrix of ARTICULAR CARTILAGE and what do they do
CHONDROCYTES
maintain a stable phenotype to retain their function as a permanent cartilage
how are COLLAGEN FIBRES at SUPERFICICAL LAYER of ARTICULAR CARTILAGE vs DEEP LAYER
PARALLEL superficially
STOOD ON THEIR ENDS at DEEP layer
- collagen fibres most RESISTANT here
ARTICULAR CARTILAGE has DIFFERENT ZONES
what does the TIDE MARK separate
CALCIFIED CARTILAGE (ZONE 4)
(zones 1-3: Tangenital, Transitional, Radial)
PROTEOGLYCANS/AGGRECAN occupy LARGE VOLUME of WATER (due to NEGATIVE charge due to GLYCOSAMINOGLYCAN CHAINS attached).
this brings about a RISE IN OSMOTIC PRESSURE and SWELLING of cartilage.
HOW IS THIS HELD TOGETHER WHEN LOAD IS APPLIED?
RESISTANCE of COLLAGEN (intact collagen fibres) in cartilage
COUNTERACTS SWELLING PRESURE and holds cartilage intact.
these features enable joints to RESIST COMPRESSIVE FORCE while MAINTAINING a HIGH TENSILE STRENGTH
SYNOVIAL FLUID is important for articular cartilage function.
what are its CHARACTERISTICS (4)
PLASMA-LIKE
LUBRICATION
to REDUCE FRICTION
supplies NUTRITION (as no bloody supply)
COMPONENTS of SYNOVIAL FLUID
- LUBRICIN - PROTEOGLYCAN
- HYALURONAN, HA (hyaluronica acid) - GLYCOSAMINOGLYCAN
(composed of the repeating sugars glucuronic acid & N-acetylglucosamine.) - PHOSPOLIPIDS
eg Phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin
LUBRICIN in SYNOVIAL FLUID (secreted by articular cartilage and synovium) is encoded by which GENE
PRG4
FUNCTION of HA in SYNOVIAL FLUID
PROVIDES VISCOSITY to synovial fluid
(role in LUBRICATION)
through its high molecular weight (0.5–3.8 106 Da) and concentration (0.1– 5mg/mL).
what do the PHOSPHOLIPIDS in SYNOVIAL FLUID provide
HYDROPHOBICITY to articular surface
& lubrication for solid-solid contact
what is VISCOSITY a measure of
INTERNAL FRICTION of a FLUID
What is SHEAR
the GREATER the FRICTION
a strain produced by pressure in the structure of a substance
the GREATER the FORCE NEEDED
VISCOSITY formula
VISCOSITY =
SHEAR STRESS / SHEAR RATE
SHEAR RATE: the measure of the FLUID SPEED compared to the SURFACE that its sliding from
SHEAR THINNING is derived from…as…
HA ALLIGNMENT MOLECULE
as the SHEER RATE INCREASES
movement of the alignment as as you move the joint
MODELS of LUBRICATION in ARTICULAR CARTILAGE:
1. SQUEEZE FILM:
as 2 surfaces are squeezed together,
FLUID is SQUEEZED OUT from the gap
generating a HYDROSTATIC PRESSURE
MODELS of LUBRICATION in ARTICULAR CARTILAGE:
2. BOOSTING/BOOSTED
eg if jumping
WATER moves INTO cartilage and so
INCREASES CONCENTRATION of HYALURONIC ACID in fluid-film
MODELS of LUBRICATION in ARTICULAR CARTILAGE:
3. ELASTOHYDRODYNAMIC
sliding MOVEMENT
DEFORMATION of the surface serves to
TRAP PRESSURIZED FLUID in 1 AREA
FLUID-FILM MECHANISMS
NO CONTACT between surfaces,
FRICTION DEPENDENT on the VISCOSITY of the Lubricant
PROVIDE the LOW FRICTION ENVIRONMENT for the
articular cartilage at physiologic loads, accomplished by creating a wedge of fluid between the two bearing surfaces.
The most desirable lubrication
BOUNDARY LUBRICATION
CHEMICAL PROPERTIES of Lubricant are NOT AS IMPORTANT as the SURFACES IN CONTACT
PREVENTS ASHESION and ABRASIONS of two surface
and is independent of the physical properties of the lubricant or contacting surfaces.
Hyaluronan and lubricin are believed to be the main boundary lubricants of the diarthrodial joint.
what is the LAMBDA RATIO a measure of
MINIMUM FILM THICKNESS (h min) required
in relation to the composite surface ROUGHNESS (Ra1, Ra2)
shown on STIBECK CURVE
friction coefficient against the bearing number μω/p (lubricant viscosity (η), speed (ω) and contact pressure (p) )
COEFFICIENT OF FRICTION is DIRECTLY PROPORTION to the VISCOSITY of the lubricant and the DIFFERENCE IN SPEED of the contact surfaces;
and INVERSELY PROPORTIONAL to the PRESSURE which is EXERTED on the contact SURFACES
*Boundary lubrication: λ ≤ 1
*Mixed lubrication: 1 < λ < 3
*Fluid film lubrication: λ ≥ 3
3 types of WEAR of articular cartilage
which lead to DISRUPTION of CARTILAGE MICROSTRUCTURE
- INTERFACIAL WEAR
Adhesion, Abrasion - FATIGUE WEAR
increase strain rate, microtrauma exceed, reparative process - HIGH IMPACT LOADING WEAR
increase Stress, Increase Strain
CHANGES in articular cartilage with WEAR:
- LOOSENING of COLLAGEN NETWORK
- PROTEOGLYCAN EXPANSION (collagen not holding it together)
- TISSUE SWELLING
- REDUCED STIFFNESS of cartilage
- INCREASED PERMEABILITY
-> abnormal:
STRESSED & STRAINS
Mechanoelectrochemical stimuli
ECM REMODELLING of CHONDROCYTES
what do the CHANGES in articular cartilage with WEAR eventually lead to
OSTEOARTHIRITIS
what is an EARLY INDICATOR of OSTEOARTHIRITIS
LOSS of PROTEOGLYCANS
Formation of clusters of activated and proliferating chondrocytes is a hallmark
in the early phase of OA cartilage
OA:
what do CHONDROCYTES SECRETE that cause ARTICULAR CARTILAGE to be LOST
what do they do
METZINCINS:
MMPs & ADAMTSs
ENZYMES that BREAK DOWN (/regulate) ECM
MMPs and ADAMTSs are part of which ENZYME FAMILY
METZINCINS
how many TYPES of MMPs and ADAMTSs are there
23 TYPES of MMPs
20 TYPES of ADAMTSs
(19 types ADAMs)
OA:
what ENZYME causes CLEAVAGE of COLLAGEN TYPE II
(cleavage removes the collagen)
CATHEPSIN K
- a lysosomal CYSTEIN PROTEASE
(involved in bone remodelling and resorption)
OA:
what do MMPs and ADAMTSs do to AGGRECAN (proteoglycan)
CLEAVE aggrecan
(Aggrecanases - break down aggrecan)
OA:
what results from CLEAVAGE of AGGRECAN by MMPs and ADAMTSs
AGGRECAN (proteoglycan) is LINKED to GLYCOSAMINOGLYCANS:
- HYALURONAN (HA)
- KERATAN SULFATE
- CHONDROITIN SULFATE
these sugars are RELEASED and escape
CAUSING SWELLING
how does ARTICULAR CARTILAGE WITHSTAND LOAD
by ATTRACTING WATER into the NEGATIVELY CHARGED PROTEOGLYCANS
